This is a book you should judge by its title. "Power trip" says all that is warped about the author and his conception of politics. To him, it is an addiction and a game, Grand Theft Auto transplanted to Westminster. As the body count from his drive-by shootings piles up, right or wrong never comes into it. As for beliefs, they are always incidental to his only important cause – engorging the influence and notoriety of Damian McBride by making himself indispensable to Gordon Brown. It tells us something ghastly about his former boss – or, rather, confirms long-held suspicions – that McBride judged that the best way to bring happiness to his master was to engage in repeated character assassinations of Labour colleagues.

McBride isn't an idiot and, when sober, he has a sophisticated mind and can turn a phrase. So in both the book and the interviews he has given to promote it, he has acknowledged how destructive he was. He seems to think that if he calls himself a "nasty bastard" often enough we will somehow find that redeeming. Some commentators have fallen for it. "At least he's honest," they have said of his confessions to practising "the dark arts of political spin" – itself a dishonest euphemism that semi-glorifies what should be called lying and smearing. Damian, the sinner repentant? I am not buying it. What about penance? Forgiveness is not found by trousering a large cheque from a rightwing newspaper so that it can serialise your repellent activities to coincide with the Labour conference. Most disgusting of all is his attempt to gain our understanding for his amoral behaviour by insinuating that the fundamental fault lies not with him, but with the "cut-throat" world of politics into which he fell, "sucked in like a concubine at a Roman orgy". Thus he seeks to present himself as some sort of victim. Pass the sickbag. It is just another of his dirty spins to try to tar everyone else in politics with his shitty brush.

There's a further reason why his claimed regrets stink of insincerity. He still sounds terrifically pleased with himself. It is with bragging relish that he details how ruthlessly he stitched up this minister or how artfully he manipulated that journalist. He tries to tempt us to admire him despite ourselves. I may have been a bad boy – this is his line – but you've got to admit I was terribly good at being wicked.

Truth to tell, he wasn't. This book can be shocking without being in the least bit surprising because its author's reputation was already well-established. He acquired the sobriquet "McPoison" when he was still in post because he was a bungling assassin who left his grubby dabs all over his victims. McBride relates how he became the prime suspect of a leak inquiry. He is interviewed by two retired detectives from special branch, whom he attempts to gull by pointing the investigators in the direction of an entirely innocent party. When they cannot prove their suspicions, McBride pats himself on the head for using a practised tactic of "lying-without-lying". Yet it is a hollow escape. He has enough self-awareness to concede that "everyone in government believed I was responsible" and "it didn't do Gordon any favours either, once people worked [it] out."

Even when he becomes semi-conscious of how appallingly and recklessly he is behaving, he is too in love with his own cunning to stop, too intoxicated with his power and his capacity to use it to hurt other people. He is also too pissed. "I was by any measure an alcoholic, albeit probably the dictionary definition of a functioning one." Not so sure about the "functioning". Having set off an uproar with a briefing about some EU negotiations, he gets utterly wasted and is therefore oblivious to the trouble he has unleashed. He wakes on the sofa at around midday to find 26 missed calls on his mobile, a number of them from Brown saying: "This. Is. Gordon. Call. Me. Immediately." On another occasion when McBride has gone missing, Ed Balls finds him lying drunk in a hotel room and resorts to dousing him with a bin of cold water.

Apart from the author, who else does this book indict? It is a poor advertisement for the civil service selection process. He got into government in the first place because he passed the entry tests. These include an interview with a psychiatrist, which is supposed to establish whether a candidate is an egomaniac, a liar or a potential security risk. As he writes, for this book is not without some wit, "at no point" were "my violent competitive streak, excess drinking, duplicitous instincts, preference for football over work" regarded as reasons not to appoint him.

People ask: "Why did no one blow the whistle?" Here was the problem. The client group of journalists who swallowed his stuff and regurgitated it into the public domain were not going to bite the hand feeding them. That left everyone else with the same difficulty as the ex-special branch detectives who quizzed him about that leak. Unless one of his collaborators was willing to speak out, it was hard to turn strong suspicions into cast-iron proof.

It was all done, says McBride, out of devotion to "the greatest man I ever met". He tells us that there was an "unspoken" understanding with his master that Brown would not "question my methods". Even if true, that is reprehensible in itself. Brown was famous for his attention to detail and his obsession with media coverage. Are we seriously to believe that he never once inquired about his spin doctor's "methods"? To my certain knowledge, Brown was given frequent and authoritative warnings. Gus O'Donnell, the cabinet secretary, urged him to dispose of McBride. Jacqui Smith, Harriet Harman, Alistair Darling and Douglas Alexander were among the many cabinet ministers who protested directly to Brown. To them all, he would claim that he knew nothing. I am prepared to believe that he was not always aware of the detail of every dirty trick if only because he decided to "look the other way", to use one of McBride's favourite phrases.

Yet here we have, from the hatchet man himself, plenty of evidence that Brown was the opposite of an innocent bystander. McBride describes one occasion when Brown instructs him to leak at a European summit. "Be careful – don't do it with any British guys." When one of McBride's schemes goes wrong, Brown asks: "Is all that business over with?" When Brown fears that a McBride leak will upset Buckingham Palace, he rings up at five in the morning screaming: "How can you do this to me? This is the Queen! THE QUEEN!" On yet another occasion when McBride has caused mayhem, Brown asks: "Why do you do this stuff?" Why? Because McBride believed that is what Brown wanted from him. After all, if Brown didn't want it, he would have sacked him.

It was Brown who created and presided over the brutish, treacherous, gangland culture in which his hitman operated. Even McBride laughs at his former capo's "comically irrational outbursts" and propensity to "unleash a tremendous volley of abuse, usually just a stream of unconnected swear words". Then there is Brown's default response to things going wrong – which is to blame someone else. "Blair!", roars Brown about a self-inflicted blunder. "Blair made me give him the figures. Why has he done this to me?"

The real villain of the period was not McBride. He was just the vicious little monkey. The organ grinder was Gordon Brown, the man who prated about his "moral compass" while allowing his smear merchant to trash the characters of colleagues. In the end, the reputation it most fouled was his own. Which is a sort of justice.

The UK book world still suffers from a sharp divide along gender lines. Take a look at the figures for the number of male and female reviewers and the authors under review in Britain's major books sections